LINKING EARLY LATE ORDOVICIAN PALEOBIOGEOGRAPHIC DATA WITH CLIMATE-OCEAN MODELS

Multivariate analyses of 38 Caradocian localities containing a total of 550 genera from around the globe indicate the presence of strong latitudinal and longitudinal gradients in taxonomic composition. Articulate brachiopods and trilobites dominate most localities with minor representation by corals, sponges, bivalves, gastropods cephalopods, and bryozoans.

Cluster analysis of the 38 localities identified five major clusters that correspond to distinct paleocontinent regions: Laurentia, Baltica, and three Gondwanan regions, China, Australia, and South Central Europe. The Chinese cluster is distinct from other tropical regions indicating strong longitudinal differentiation in taxonomic composition among regions in the tropics. Latitudinal differentiation among regions is best shown by the relationships among Laurentia (tropical), Baltica (intermediate latitudes), and South Central Europe (high latitudes). This relationship is supported by detrended correspondence analysis showing the localities from these regions arrayed along an axis from low to high latitudes. Latitudinal differentiation among these three regions appears to reflect a diversity gradient from high diversity in the tropics to low diversity at high latitudes and taxonomic differences, such as abundant corals at low latitudes and a lack of corals at high latitudes.

The spatial distribution of Caradocian marine organisms is consistent with climatic and oceanographic gradients inferred from coupled ocean-climate models. These models indicate that the Caradocian ocean-climate system was dominated by strong latitudinal temperature gradients and vigorous horizontal and vertical ocean circulation. The paleobiogeographic data thus provide an important corroboration of the global ocean-climate models and lead to a more robust inference of the early Late Ordovician global ecosystem.